U.S. patent application number 13/249770 was filed with the patent office on 2012-08-30 for method and apparatus for reducing liner slot plugging tendencies.
Invention is credited to Denis Gilbert, Simon D. Gittins, Subodh Gupta, Arnoud Struyk.
Application Number | 20120217005 13/249770 |
Document ID | / |
Family ID | 45893850 |
Filed Date | 2012-08-30 |
United States Patent
Application |
20120217005 |
Kind Code |
A1 |
Gupta; Subodh ; et
al. |
August 30, 2012 |
METHOD AND APPARATUS FOR REDUCING LINER SLOT PLUGGING
TENDENCIES
Abstract
A slotted liner having straight-cut liner slots with a wall
roughness which does not exceed 1 .mu.m. A slot cutting method to
produce smooth slots using a specified blade configuration,
rotational speed, and feed rate.
Inventors: |
Gupta; Subodh; (Calgary,
CA) ; Struyk; Arnoud; (Calgary, CA) ; Gilbert;
Denis; (Airdrie, CA) ; Gittins; Simon D.;
(Bragg Creek, CA) |
Family ID: |
45893850 |
Appl. No.: |
13/249770 |
Filed: |
September 30, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61388099 |
Sep 30, 2010 |
|
|
|
Current U.S.
Class: |
166/227 ;
83/54 |
Current CPC
Class: |
E02B 11/005 20130101;
E21B 43/086 20130101; Y10T 83/0596 20150401; B23D 45/122 20130101;
E03B 3/18 20130101 |
Class at
Publication: |
166/227 ;
83/54 |
International
Class: |
E03B 3/18 20060101
E03B003/18; B26D 3/00 20060101 B26D003/00 |
Claims
1. A process for mechanically creating a slot in and through a
metal material in such a way as to ensure that the maximum
roughness of the two long sides of the slot wall thus created,
hereinafter referred to as the wall roughness, is 2 .mu.m
(micrometers), the process comprising: employing a hard-surface
circular cutting blade with a sufficient number of teeth to permit
the creation of a slot wall, the roughness of whose long sides do
not exceed 2 .mu.m, but with the number of cutting blade teeth
limited so as to avoid tooth failure due to elevated stresses in
the blade periphery between teeth; operating the circular blade at
a rate of 165 to 1600 RPM; maintaining the feed rate in the range
of 0.25 to 0.7 inches per minute; and using a circular cutting
blade with the number of teeth ranging between 72 and 160.
2. The process of claim 1 wherein the circular cutting blade has 72
teeth on its periphery.
3. The process of claim 1 wherein the circular blade is operated at
a rate of, or close to, 1600 rpm.
4. The process of claim 1 wherein the feed rate is at or close to
0.5 inches per minute.
5. The process of claim 1 wherein the slots are cut through the
wall of a metal pipe.
6. The process of claim 1 wherein the wall roughness of the slot is
less than or equal to 1 .mu.m.
7. A method of cutting a plurality of slots into a tubular member,
each slot having two long sides with a maximum roughness of
substantially 2 .mu.m, the method comprising: providing a circular
blade having between about 72 and about 160 teeth; operating the
circular blade at a rate of between about 165 and about 1600 RPM;
and feeding the tubular into the blade at a feed rate of between
about 0.25 and about 0.7 inches per minute.
8. The method of claim 7 wherein the slots are cut with one pass of
the blade.
9. The method of claim 7 wherein the blade has substantially 72
teeth.
10. The method of claim 7 wherein the blade is composed of tungsten
carbide.
11. The method of claim 7 wherein the blade is composed of high
speed steel.
12. The method of claim 7 wherein the rote is substantially 1600
RPM.
13. The method of claim 7 wherein the feed rate is substantially
0.5 inches per minute.
14. The method of claim 7 wherein the maximum roughness of the long
sides is substantially 1 .mu.m.
15. The method of claim 7 wherein the plurality of slots are cut to
provide an open area in the tubular member of substantially
2.25%.
16. The method of claim 7 further comprising cooling the blade.
17. The method of claim 7 further comprising administering cutting
fluid to the blade.
18. The method of claim 17 wherein the cutting fluid is ECO 7001
from Fuchs Lubricants.
19. The method of claim 17 wherein administration of the cutting
fluid is by misting.
20. A metal tubular comprising: an exterior surface; an interior
surface disposed internally relative to the exterior surface; and a
plurality of slots extending between the exterior surface and the
interior surface, the plurality of slots having long sides, the
long sides having a maximum surface roughness of 2 .mu.m.
21. The metal tubular of claim 20 wherein the maximum surface
roughness of the long sides is 1 .mu.m.
22. The metal tubular of claim 20 wherein the plurality of slots
provide an open area of substantially 2.25%.
23. A slotted liner for production of petroleum fluids from a
bitumen formation, the slotted liner comprising: an exterior
surface; an interior surface disposed internally relative to the
exterior surface; and a plurality of slots extending between the
exterior surface and the interior surface, the plurality of slots
having long sides, the long sides having a maximum surface
roughness of 2 .mu.m.
24. The slotted liner of claim 23 wherein the maximum surface
roughness of the long sides is 1 .mu.m.
25. The slotted liner of claim 23 wherein the plurality of slots
provide an open area of substantially 2.25%.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of and priority from
U.S. Provisional Patent Application No. 61/388,099 filed Sep. 30,
2010, which is incorporated herein by reference in its
entirety.
FIELD
[0002] The present disclosure relates generally to oil production.
More particularly, the present disclosure relates to slotted liner
and the cutting of slots for slotted liner for heavy oil
production.
BACKGROUND
[0003] One of the key downhole devices for preventing or reducing
the entry of unwanted solids into the interior of a wellbore is the
slotted liner. Typically, in the petroleum industry, this is a
steel pipe into which slots have been cut or machined entirely
through the steel pipe wall, the slots being of a particular
geometry and set of dimensions and being distributed along the pipe
according to a prescribed pattern.
[0004] The traditional liner slot involves a geometry whereby the
width of the slot remains constant throughout the depth of the slot
(i.e., from exterior to interior surface of the pipe). The
advantage of this "straight-cut" liner slot geometry is that its
manufacture requires only a single pass of a rotating cutting
blade.
[0005] In the petroleum industry, conventional methods of machining
slots in slotted liners employ the use of standard high speed steel
tooth-bearing cutting blades, producing a slot surface with a
relatively rough finish, for example having a Ra of 4-8 .mu.m or
4-6 .mu.m. Slotted liners with conventionally machined slots, and
associated Ra values, tend to plug over time as a consequence of
this roughness so that the total available inflow area is reduced
along with the overall productivity of the well.
[0006] To compensate for this slot plugging tendency over time, and
the corresponding reduction in inflow area, conventional slotted
liners are machined such that they possess an excess number of
slots. The excess number of slots adds to the overall cost of
producing slotted liners weakens the liners, while not necessarily
extending their efficient life span.
[0007] One slotted liner manufacturer's website indicates that, for
example, the area of a slotted liner occupied by slots, the open
area, may be in the order of 3%. The number of slots required (per
foot of length) may be calculated from the formula below:
N=12.pi.DC/100WL
[0008] Where D is the OD of the liner, in inches. C is the selected
open area, in percent. W is the selected slot width, in inches, and
L is the slot length, in inches.
[0009] Thus, for a 3% open area in a 4.5'' OD liner, utilizing
0.020'' wide slots 1.5'' long, 170 slots would be required per foot
(172 rounding to the next higher multiple of four as it is
customary to provide 4 rows of slots per foot).
[0010] Conventional slotted liners require back flushing and acid
cleaning in an effort to open up plugged slots, a method that may
or may not be successful. Where these remedial techniques are not
effective in restoring slot transmissivity, it may be necessary to
abandon the well or re-drill the well and install a new slotted
liner system.
[0011] A discussion of the slot plugging problem is presented in
U.S. Patent Publication No. 2009/0014174 titled "Use of Coated
Slots For Control Of Sand Or Other Solids In Wells Completed For
Production Of Fluids", Inventor E. Douglas Hollies, filed Dec. 28,
2007. Under "Summary Of Invention", Paragraph 21, it states:
[0012] "Our investigations have revealed that slot plugging occurs
when the flour-like fines that are resident within the sand
reservoir pore spaces move into the slot, adhere to the slot wall,
and eventually back up into the sand bridge at the entry to the
slot. This adherence of fines to the slot wall is caused or
facilitated by the uneven surface of the wall, whose irregular
features we refer to as striations, resulting from, among other
things, the blade cutting of the slots described earlier."
[0013] Thus, the experimental investigations carried out by Hollies
clearly support the conclusion that wall roughness is a major
factor in slot plugging.
[0014] The solution to the slot wall roughness problem proposed by
Hollies involves application of a coating to the slot walls so as
to cover the uneven wall surface to provide for smooth wall
surfaces. This approach entails additional cost associated with
purchasing and application of the coating material.
[0015] A well-known industry approach aimed at circumventing the
plugging problem involves the use of keystone slots, or of
geometries which approximate the principal feature of a keystone
slot.
[0016] A keystone slot has a smaller width on the upstream side
(i.e., outside surface in the case of a producing well) of the pipe
than on the downstream side (i.e., inside surface in the case of a
producing well) of the pipe. The intent is that a solid particle,
once having passed through the entry of the slot, which is its
narrowest point, is thereafter unlikely to become lodged in the
slot where it can aid and abet plugging. However, a disadvantage of
the keystone slot is that its manufacture requires two passes of
the cutting blades, each at a different angle, to achieve the
variable-width slot cross-section. This creates difficulties in
maintaining slot widths within acceptable tolerances.
[0017] An alternative to the keystone slot which is nonetheless
aimed at achieving the advantage of a narrower entry combined with
a wider exit is described in a number of patents. These include
U.S. Pat. No. 6,112,570 issued Sep. 5, 2000 and titled "Method For
Making Slots In Metal Pipe", Canadian Patent No. 2,183,032 issued
Jul. 17, 2001 and titled "Method For Making Slots In Metal Pipe",
and Canadian Patent No. 2,324,730 issued Aug. 12, 2003 and titled
"Method And Apparatus For Reducing Slot Width in Slotted Tubular
Liners". These methods begin with a straight cut slot and then
narrow the aperture of the slot entry by means of force exerted on
the longitudinal edge of the slot or on the outer surface of the
pipe in the vicinity of the slot so as to re-shape the slot and
specifically to narrow its width at the exterior surface. A further
such alternative is described in U.S. Pat. No. 7,069,657 issued
Jul. 4, 2006 and titled "Method To Reduce The Width Of A Slot In A
Pipe Or Tube" which subjects the metal surface to impingement or
bombardment by balls, thereby achieving the narrowing of slot width
while avoiding some of the machining alignment and the coordination
problems associated with the prior methods cited above. Thus, while
the geometric advantage of a keystone slot can be approximated
using techniques that deform (i.e., narrow) the exterior (upstream)
slot width, they too involve their own set of manufacturing
problems.
[0018] An additional invention dealing with variable width slots is
described in U.S. Pat. No. 5,046,892 issued Sep. 10, 1991 and
titled "Apertured Pipe Segment". However, this patent is concerned
with plastics and with a manufacturing technique which is specific
to plastics and is not applicable to the operating environment of
steel slotted liners in the petroleum industry.
SUMMARY
[0019] It is an object of the present disclosure to obviate or
mitigate at least one disadvantage of previous methods and
apparatus for reducing liner slot plugging tendencies.
[0020] The present disclosure, hereinafter referred to as the
Subject Disclosure, relates to the prescription of a maximum level
of slot wall roughness (Ra), and associated geometry, that affords
a more favorable environment for flow through the slot, along a
manufacturing method by which these prescribed conditions can be
achieved practically. In this document. Ra refers to the roughness
of the long walls of the slot.
[0021] The Subject Disclosure is based firstly on a finding,
through experimental investigations, that a significant reduction
in flow regime instability, and consequent liner slot plugging
tendency, can be achieved by using a slotted liner having
straight-cut slots in which Ra is reduced to 2 .mu.m or lower. The
Subject Disclosure is based secondly on our identification of an
efficient and economic means of achieving this reduced Ra through
machining techniques which entail neither the addition of a smooth
coating on the slot wall, nor the multiple-pass procedure required
in creating a keystone slot, nor the application of special
techniques, as described above, to narrow the slot entrance and
thereby approximate the effect of a keystone slot.
[0022] The Subject Disclosure, in the first instance, utilizes the
finding that straight-cut slots with a Ra of less than 2 .mu.m will
permit significantly less sand production than slots with greater
Ra. The Subject Disclosure also includes a method of manufacturing
such slots.
[0023] In fact, while the Ra maximum criterion, as determined from
experimental results described above, is 2 .mu.m, an embodiment of
the Subject Disclosure a slot manufacturing technique for
manufacturing slotted liners with an Ra of 1 .mu.m.
[0024] A further embodiment of the Subject Disclosure is an
uncoated straight-cut liner slot wherein Ra does not exceed 2
.mu.m, and which can be manufactured with an Ra of 1 .mu.m, and a
manufacturing means by which this is achieved.
[0025] A means by which this slot geometry and smoothness is
achieved involves machining of the slots using special cutting
means, such as, for example, a circular cutting blade of specified
metallurgy with a specified range of cutting tooth size, a
specified range of blade speed and a specified range of feed
rates.
[0026] Thus the Subject Disclosure dictates a maximum Ra and
creates a slot with a Ra value that does not exceed the maximum Ra
so as to avoid or mitigate the solids plugging problem. This
mitigating result is achieved while retaining the manufacturing
simplicity and finer tolerances attainable with a straight-cut
slot, avoids the added manufacturing cost and weakness of having a
high open area, avoids the added manufacturing cost and tolerance
problems associated with a keystone slot, avoids the alignment and
coordination problems associated with narrowing the slot
cross-section at its exterior, and avoids the additional cost of
applying a suitable coating to achieve slot wall smoothness.
[0027] In a first aspect, the present disclosure provides a process
for mechanically creating a slot in and through a metal material in
such a way as to ensure that the maximum roughness of the two long
sides of the slot wall thus created, hereinafter referred to as the
wall roughness, is 2 .mu.m (micrometers), the process including
employing a hard-surface circular cutting blade with a sufficient
number of teeth to permit the creation of a slot wall, the
roughness of whose long sides do not exceed 2 .mu.m, but with the
number of cutting blade teeth limited so as to avoid tooth failure
due to elevated stresses in the blade periphery between teeth,
operating the circular blade at a rate of 165 to 1600 RPM,
maintaining the feed rate in the range of 0.25 to 0.7 inches per
minute, and using a circular cutting blade with the number of teeth
ranging between 72 and 160.
[0028] In an embodiment disclosed, the circular cutting blade has
72 teeth on its periphery. In an embodiment disclosed, the circular
blade is operated at a rate of, or approximately, 1600 rpm.
[0029] In an embodiment disclosed, the feed rate is at or
approximately 0.5 inches per minute.
[0030] In an embodiment disclosed, the slots are cut through the
wall of a metal pipe, for example an Oil Country Tubular Good
(OCTG), such as casing or liner for mechanical completion of an oil
well.
[0031] In an embodiment disclosed, the wall roughness of the slot
is less than or equal to 1 .mu.m.
[0032] In a further aspect, the present disclosure provides a
method of cutting a plurality of slots into a tubular member, each
slot having two long sides with a maximum roughness of
substantially 2 .mu.m, the method including providing a circular
blade having between about 72 and about 160 teeth, operating the
circular blade at a rate of between about 165 and about 1600 RPM,
and feeding the tubular into the blade at a feed rate of between
about 0.25 and about 0.7 inches per minute.
[0033] In an embodiment disclosed, the slots are cut with one pass
of the blade.
[0034] In an embodiment disclosed, the blade has substantially 72
teeth. In an embodiment disclosed, the blade is composed of
tungsten carbide. In an embodiment disclosed, the blade is composed
of high speed steel.
[0035] In an embodiment disclosed, the rate is substantially 1600
RPM.
[0036] In an embodiment disclosed, the feed rate is substantially
0.5 inches per minute.
[0037] In an embodiment disclosed, the maximum roughness of the
long sides is substantially 1 .mu.m.
[0038] In an embodiment disclosed, the plurality of slots are cut
to provide an open area in the tubular member of substantially
2.25%.
[0039] In an embodiment disclosed, the method further includes
cooling the blade while cutting. In an embodiment disclosed, the
method further includes administering cutting fluid to the blade
prior to or during cutting or both. In an embodiment disclosed, the
cutting fluid is ECO 7001 from Fuchs Lubricants. In an embodiment
disclosed, the cutting fluid is administered by misting.
[0040] In a further aspect, the present disclosure provides a metal
tubular having an exterior surface, an interior surface disposed
internally relative to the exterior surface, and a plurality of
slots extending between the exterior surface and the interior
surface, the plurality of slots having long sides, the long sides
having a maximum surface roughness of 2 .mu.m.
[0041] In an embodiment disclosed, the maximum surface roughness of
the long sides is 1 .mu.m.
[0042] In an embodiment disclosed, the plurality of slots provide
an open area of substantially 2.25 percent.
[0043] In a further aspect, the present disclosure provides a
slotted liner for production of petroleum fluids from a bitumen
formation, the slotted liner having an exterior surface, an
interior surface disposed internally relative to the exterior
surface, and a plurality of slots extending between the exterior
surface and the interior surface, the plurality of slots having
long sides, the long sides having a maximum surface roughness of 2
.mu.m.
[0044] In an embodiment disclosed, the maximum surface roughness of
the long sides is 1 .mu.m.
[0045] In an embodiment disclosed, the plurality of slots provide
an open area of substantially 2.25%.
[0046] Other aspects and features of the present disclosure will
become apparent to those ordinarily skilled in the art upon review
of the following description of specific embodiments in conjunction
with the accompanying figures.
BRIEF DESCRIPTION OF THE DRAWINGS
[0047] Embodiments of the present disclosure will now be described,
by way of example only, with reference to the attached Figures.
[0048] FIG. 1 is a plot of sand production versus Ra for oil flow
in accordance with the present disclosure;
[0049] FIG. 2 is a plot of average sand production through slot
versus average slot pressure drop across slot wall roughness
categories for liquid flow experiments in accordance with the
present disclosure;
[0050] FIG. 3 is a plot of experimental correlatability versus
roughness for flow stability in accordance with the present
disclosure;
[0051] FIG. 4 is a profile view of a slot cutting blade in
accordance with the present disclosure;
[0052] FIG. 5 is an end view of a slotting process of the present
disclosure, for longitudinal slots;
[0053] FIG. 6 is an end view of a slotting process of the present
disclosure, for transverse slots;
[0054] FIG. 7 is cross-section view of FIG. 5 along 7-7;
[0055] FIG. 8 is a detail of a slot of FIG. 7;
[0056] FIG. 9 is a cross-section view of FIG. 6 along 9-9;
[0057] FIG. 10 is a detail of a slot of FIG. 9;
[0058] FIG. 11 is a slotted liner of the present disclosure having
longitudinal slots; and
[0059] FIG. 12 is a slotted liner of the present disclosure having
transverse slots.
DETAILED DESCRIPTION
[0060] Generally, the present disclosure provides a method and
apparatus for reducing liner slot plugging tendencies.
[0061] In a petroleum well, when production fluid flows from the
annulus through the slots of a liner into the production tubing,
the slot plugging phenomena will be evidenced by an increase in the
pressure drop delta-P (.DELTA.P) across the slots (i.e. pressure
differential between the annulus and the inner bore of the
production tubing). A non-obstructed slot will allow free flow of
particles small enough to pass through the slot.
[0062] Experimental Data
[0063] Experimental results were obtained through confidential
laboratory tests. Fluid-sand flow tests were carried out using a
fluid mixture of oil and water (O,W) in volume ratios that varied
from 40.0 cc/hr (O,W) to 160.320 cc/hr (O,W). The fluid mixture was
forced through a cylinder filled with sand, silt and clay. One end
of the cylinder includes a slot being tested. The other end is
connected to the fluid mixture (O,W). The fluid mixture is pumped
under pressure through the cylinder sand, silt and clay, and exits
through the test slot. During the test, both .DELTA.P across slot
and sand, silt and clay are recorded.
[0064] FIG. 1 is a plot of results of the fluid-sand flow tests
comparing slots over a wide range of roughness values. The slots
exhibit progressively higher sand production levels as slot wall
roughness increases. However, the results are fairly continuous,
and even generally linear, and provide no indication of a preferred
maximum Ra.
[0065] FIG. 2 is a plot of average results, across all tested Ra
values, illustrating the expected correlation between sand
production levels and average slot pressure drop. This confirms the
nature of the plugging mechanism, as described above, and provides
additional verification of the reliability of the testing
procedure, but otherwise offers no new insights. The data points in
FIG. 2 have the following Oil (q.sub.o) and Water (q.sub.w) flow
rates per average slot pressure drop (.DELTA.P):
TABLE-US-00001 q.sub.o (cc/hr) q.sub.w (cc/hr) Average .DELTA.P
(psi) 40 0 0.10 80 0 0.12 120 0 0.16 160 0 0.19 160 80 0.51 160 160
0.62 160 240 0.68 160 320 0.72
[0066] However, in examining the correlation between sand
production and pressure drop, it was noted that, as Ra increases,
the flow regime exhibits a progressively higher degree of
experimental variance, which is indicative of flow regime
instability. As a measure of this variance characteristic, or more
specifically of inverse variance, the correlations of sand
production versus pressure drop were examined over a range of Ra
values, and the coefficient of determination (R.sup.2) was
calculated. A R.sup.2 of 1.0 implies perfect correlation and a
R.sup.2 of zero implies a total lack of correlation.
[0067] FIG. 3 is a plot of observed R.sup.2 values against Ra. As
indicated, there is a trend break, or substantial trend
non-linearity, in the vicinity of Ra=2 .mu.m. This suggests there
is not only a quantitative difference but also a broad qualitative
distinction between slots whose wall roughness values are above or
below a value of some 2 .mu.m. Specifically, over a continuous
range of Ra values, the corresponding change in magnitude of the
coefficient of determination is abrupt rather than continuous or
gradational.
[0068] The experimental results thus establish firstly, a smooth or
gradational correlation between Ra and sand production, and an
abruptly changing or non-gradational correlation between Ra and
flow regime stability, as indicated by the coefficient of
determination. The existence the abrupt or non-gradational
correlation and the specific roughness value at which this abrupt
change occurs are surprising.
[0069] An embodiment of the Subject Disclosure thus applies the
non-linear experimental outcome that there is material advantage in
maintaining Ra at values of slots in a slotted liner at 2 .mu.m or
less.
[0070] Manufacture of Slotted Liners
[0071] An embodiment of the Subject Disclosure is an efficient
means of manufacturing slotted liners having slots with an Ra<1
.mu.m.
[0072] FIG. 4 is a blade 60 representative of one type of blade
used with the present disclosure. In an embodiment, the blade 60 is
made of high impact tungsten carbide. In an embodiment, the blade
60 has a number of teeth 20. In an embodiment, the teeth are
profiled in a direction aligned perpendicular to the axis or
rotation. In FIG. 4, the blade 60 has a number of teeth 20 directed
clockwise, and in operation the blade 60 would be rotated
clockwise. The number of teeth 20 in FIG. 4 number 52, which is
merely one example for the number of teeth.
[0073] The blade 60 is used to produce slots with a surface finish
Ra<1 .mu.m. Conventional slot cutting methodology is improved by
employing the blade having a selected number of cutting teeth at a
selected RPM with a selected feed rate. Performance results
indicate optimum values to select for the number of teeth,
rotational speed (RPM) and feed rate. In an embodiment of the
present disclosure, an Ra less than 1 .mu.m is achieved by cutting
slots with the speed of the blade 60 in the range of 165 to 1600
RPM and a typical feed rate in the range of 0.25 to 0.7
inch/minute.
[0074] The prescribed number of teeth 20 is based on running tests
with cutting blades 60 with coarse teeth 20, at an intermediate
level with 72 teeth 20, and on the fine end with 100 and 160 teeth
20. The diameter of the blades tested was 3'' but 4'' blades may
also be used. In an embodiment disclosed, the rotational speed
(RPM) selected for 3'' blades is reduced by the ratio of actual
blade size. For example, 165 to 1600 RPM for 3'' diameter blades
would convert to approximately 124 RPM to 1200 RPM, in order to
maintain approximately the equivalent linear velocity of the teeth
20 at the circumference of the blade 60.
[0075] The lifespan of the blades 60 with teeth 20 numbering 100
and 160 teeth was limited as measured by the advent of teeth 20
that broke. The breakage of the teeth 20 occurred because the
material in the root of the teeth 20 was not strong enough to
withstand the force exerted on the root during the slot
manufacturing process. After testing blades with 100 and 160 teeth
we stepped down to 72 teeth blades to reduce the effect of stress
at the root of the teeth to tolerable levels. While the number of
teeth could be reduced below 72 from a stress perspective, the
result would be a slot of greater Ra than that achieved using the
tested configuration. Generally, the fewer teeth present on a
blade, the greater the resulting Ra of slots cut by the blade.
Correspondingly, it may be feasible to employ a moderate increase
in the number of teeth above 72 while avoiding the above-noted
problem with stress raising and structural weakness.
[0076] In an embodiment disclosed, the desired ultimate surface
finish in the Ra range of 0.8-1 .mu.m is achieved by means of a
combination of a cutting blade rotation rate of some 1600 RPM, a
blade feed rate of 0.5 inches per minute, and a cutting wheel
having about 72 teeth. A special cutting fluid, such as that
manufactured by Fuchs Lubricants with designation ECO 7001, applied
through a mister system to provide lubrication and at the same time
remove cuttings from the blade teeth, may be used to reproduce
these results. The blade may also be cooled during cutting using
lubrication and techniques as described above. This process will
minimize the number of cuttings to be tracked around by the blade
and score the opposite side of the slot. It is important to not
allow cuttings to remain embedded within the roots of the teeth
with consequent scoring. With respect to the cutting blade, an
embodiment involves the use of tungsten carbide (Micrograin)
blades. However, a less costly blade style, for example high speed
steel (HSS), which may contain a cobalt additive to improve
strength and increase cutting blade lifespan.
[0077] Rotation rate and feed rate have a direct effect on both
finished quality of surface roughness and lifespan of the blade.
The commercial RPM recommended for a tungsten carbide blade is 1150
RPM with adequate cooling. For HSS (cobalt enriched) recommended
RPM is .about.500 RPM and for HSS (not cobalt enriched),
recommended RPM is .about.200 RPM. Typical feed rates during
testing ranged from 0.25-0.86 inches/min (0.1-0.36 mm/sec).
[0078] FIGS. 5, 7, and 8 depict a tubular member 20 having an
exterior surface 30 and an interior surface 40. A blade 60, is
aligned with the longitudinal axis of the tubular member 20 in
order to cut longitudinal slots 50.
[0079] The blade 60 is rotated at a rotational speed (RPM) 100 and
a feed rate 90 as indicated above is used. A cutting fluid 110 is
provided to the cutting area. The resulting slot 50 has a surface
finish of 0.8 to 1 .mu.m on the long side 80.
[0080] FIGS. 6, 9, and 10 depict a tubular member 20 having an
exterior surface 30 and an interior surface 40. A blade 60, is
aligned perpendicular to the longitudinal axis of the tubular
member 20 in order to cut transverse slots 50.
[0081] The blade 60 is rotated at a rotational speed (RPM) 100 and
a feed rate 90 as indicated above is used. A cutting fluid 110 is
provided to the cutting area. The resulting slot 50 has a surface
finish of 0.8 to 1 .mu.m on the long side 80.
[0082] Thus, the Subject Disclosure, as described in the above
embodiments, allows use of a simpler and more efficient
manufacturing method to manufacture straight-cut liner slots. The
method utilizes a technique which results in slots with an Ra that
does not exceed 1 .mu.m and thereby fabricate the slotted liner
with fewer slots in total, compared with standard industry
practice, while maintaining the overall design inflow area.
[0083] Smooth-Slot Slotted Liners for Wellbore Completion
[0084] FIGS. 11 and 12 are typical slotted liners 10 of the present
disclosure including a tubular member 20 having an exterior surface
30 and an interior surface 40 and a plurality of slots 50 extending
there between. The slots 50 are typically longitudinal (FIG. 7) or
transverse (FIG. 8) or a combination thereof (not shown). The
slotted liners produced by the above techniques have an Ra of below
2 .mu.m and in some embodiments below 1 .mu.m. This Ra value is
achieved without the use of coatings and with only one pass of a
cutting blade. The smoothness of the slots reduces plugging while
maintaining a lower percentage open area than would be required to
maintain a selected flow rate on a slotted liner having slots with
a greater Ra. A lower percentage open area provides two benefits:
lowered cost of production because of fewer slots being cut, and a
greater strength of a slotted liner because of the presence of
fewer slots.
[0085] In an embodiment of the present disclosure, the open area
may be reduced by as much as 25% while providing a hydraulically
similar (pressure drop) as in standard slotted liners and lower
open area resulting in a lower cost to manufacture the slots (less
slot cutting) and improved mechanical strength (less wall material
removed). In an embodiment of the disclosure, utilizing a 2.25%
open area, 128 slots per foot would be required, down from the 172
required for 3% open area (as above) for 4.5'' OD liner with slots
0.020'' wide and 1.5'' long.
[0086] In the preceding description, the slots are described as
straight-cut slots. However, the disclosure may be applied in
relation to keystone-cut slots, as well as keystone-formed slots
(such as those made by making straight cut slots or keystone-cuts
slots and then transversely or longitudinally cold working the
exterior of the slotted liner, such as by cold rolling).
[0087] In the preceding description, for purposes of explanation,
numerous details are set forth in order to provide a thorough
understanding of the embodiments. However, it will be apparent to
one skilled in the art that these specific details are not
required.
[0088] The above-described embodiments are intended to be examples
only. Alterations, modifications and variations can be effected to
the particular embodiments by those of skill in the art without
departing from the scope, which is defined solely by the claims
appended hereto.
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